The Elastoplastic Soil Material feature is used to model stress-strain relationships that are nonlinear even at infinitesimal strains. It is available in the Solid Mechanics interface. This material model requires a Geomechanics Module license (see
https://www.comsol.com/products/specifications/).
Elastoplastic Soil Material is available for 3D, 2D, and 2D axisymmetry.
By adding the following subnodes to the Elastoplastic Soil Material node you can incorporate other effects:
Add an External Stress node in case you need to define a pore pressure in a porous soil. The
Pore pressure pA is user-defined by default. The default value is 1 atm, but you can change it to another value or expression for the pore fluid pressure. If there are other physics interfaces (like Darcy’s Law) in the model that make a pressure variable available, such variables will be available in the list.
The Global coordinate system is selected by default. The
Coordinate system list contains any additional coordinate systems that the model includes (except boundary coordinate systems). The coordinate system is used when stresses or strains are presented in a local system. The coordinate system must have orthonormal coordinate axes, and be defined in the material frame. Many of the possible subnodes inherit the coordinate system settings.
Select a Material model from the list:
Modified Cam-Clay,
Modified Structured Cam-Clay,
Extended Barcelona Basic, or
Hardening Soil.
All elastoplastic soil models have density as an input. The default Density ρ uses values
From material. For
User defined enter another value or expression.
If any material in the model has a temperature dependent mass density, and From material is selected, the
Volume reference temperature list will appear in the
Model Input section. As a default, the value of
Tref is obtained from a
Common model input. You can also select
User defined to enter a value or expression for the reference temperature locally.
The Modified Cam-Clay options adds the equations and interface for defining the material properties for the modified Cam-Clay soil model.
From the Specify list, define the elastic properties either in terms of
Poisson’s ratio or
Shear modulus.
The defaults for the Poisson’s ratio ν or the
Shear modulus G,
Density ρ,
Slope of critical state line M,
Swelling index κ,
Compression index λ,
Initial void ratio e0 , and
Void ratio at reference pressure eref are taken
From material. For
User defined enter other values or expressions
Enter a value or expression for the Reference pressure pref, and the
Initial consolidation pressure pc0.
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For the Slope of critical state line you can alternatively select Match to Mohr-Coulomb criterion or Match to Matsuoka-Nakai criterion, which then matches the slope of the virgin consolidation line to the angle of internal friction. Then select the Angle of internal friction as From material or User defined.
For the Initial void ratio, you can alternatively select From void ratio at reference pressure, which then computes the initial void ratio from the reference pressure, the void ratio at reference pressure, the initial consolidation pressure, and the swelling and compression indexes. Then select the Void ratio at reference pressure eref as From material or User defined. See also The Modified Cam-Clay Soil Model in the Structural Mechanics Theory chapter.
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From the Specify list, define the elastic properties either in terms of
Poisson’s ratio or
Shear modulus.
The defaults for the Poisson’s ratio ν or the
Shear modulus G,
Density ρ,
Slope of critical state line M,
Swelling index for structured clay κs,
Compression index for destructured clay λd,
Angle of internal friction ,
Initial structure strength pbi,
Destructuring index for volumetric deformation dv,
Destructuring index for shear deformation ds,
Plastic potential shape parameter ξ,
Initial void ratio e0,
Void ratio at reference pressure for destructured clay erefd,
Additional void ratio at initial yielding Δei, and
Critical equivalent deviatoric plastic strain edcp are taken
From material. For
User defined enter other values or expressions.
Enter a value or expression for the Reference pressure pref, and the
Initial consolidation pressure pc0.
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For the Slope of critical state line you can alternatively select Match to Mohr-Coulomb criterion or Match to Matsuoka-Nakai criterion, which then matches the slope of the virgin consolidation line to the angle of internal friction. Then select the Angle of internal friction as From material or User defined.
For the Initial void ratio, you can alternatively select From void ratio at reference pressure for destructured clay, which then computes the initial void ratio from the reference pressure, the void ratio at reference pressure for destructured clay, the initial consolidation pressure, and the swelling and compression indexes. Then select the Void ratio at reference pressure for destructured clay erefd as From material or User defined. See also The Modified Structured Cam-Clay Soil Model in the Structural Mechanics Theory chapter.
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The defaults for the Poisson’s ratio ν or the
Shear modulus G,
Density ρ,
Slope of critical state line M,
Swelling index κ,
Swelling index for changes in suction κs,
Compression index at saturation λ0,
Compression index for changes in suction λs,
Angle of internal friction ,
Weight parameter w,
Soil stiffness parameter m,
Plastic potential shape parameter bs,
Tension to suction ratio k,
Initial void ratio e0,
Void ratio at reference pressure and saturation eref0, and
Initial yield value for suction sy0 are taken
From material. For
User defined enter other values or expressions.
Enter a value or expression for the Initial suction s0,
Suction s, the
Reference pressure pref, and the
Initial consolidation pressure pc0.
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For the Slope of critical state line you can alternatively select Match to Mohr-Coulomb criterion or Match to Matsuoka-Nakai criterion, which then matches the slope of the virgin consolidation line to the angle of internal friction. Then select the Angle of internal friction as From material or User defined.
For the Initial void ratio, you can alternatively select From void ratio at reference pressure and saturation, which then computes the initial void ratio from the reference pressure, the void ratio at reference pressure and saturation, the initial consolidation pressure, and the swelling and compression indexes. Then select the Void ratio at reference pressure and saturation eref0 as From material or User defined. See also The Extended Barcelona Basic Soil Model in the Structural Mechanics Theory chapter.
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The defaults for the Reference stiffness for primary loading E50ref,
Reference stiffness for unloading and reloading Eurref,
Elastoplastic compression modulus Kc,
Poisson’s ratio ν, Density ρ,
Stress exponent m,
Cohesion c,
Angle of internal friction ,
Dilatation angle ψ,
Ellipse aspect ratio R, and
Initial void ratio e0 are taken
From material. For
User defined enter other values or expressions. The
Ellipse aspect ratio R can also be defined from the
Coefficient of earth pressure at rest k0nc.
Enter a value or expression for the Failure ratio Rf, the
Reference pressure pref, and the
Initial consolidation pressure pc0.
Select the Include dilatancy cutoff check box if needed. The defaults for the
Maximum void ratio emax is taken
From material. For
User defined enter other value or expression. Enter a value or expression for the
Initial volumetric strain εvol0.
The default is None. Select
Implicit Gradient to add nonlocal regularization to the equivalent plastic strain. Enter a value for the:
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Length scale, lint. The length scale should not exceed the maximum element size of the mesh.
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Nonlocal coupling modulus, Hnl. This stiffness is the penalization of the difference between the local and nonlocal variables. A larger value enforces the equivalent plastic strain εpe to be closer to the nonlocal equivalent plastic strain εpe,nl.
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If a study step is geometrically nonlinear, the default behavior is to use a large strain formulation in all domains. Select the Geometrically linear formulation check box to always use a small strain formulation, irrespective of the setting in the study step.
Select the Calculate dissipated energy check box as needed to compute the energy dissipated by
Creep,
Plasticity,
Viscoplasticity, or
Viscoelasticity.
To display this section, click the Show More Options button (
) and select
Advanced Physics Options in the
Show More Options dialog box.
This section is available with the Implicit gradient nonlocal plasticity model. Select the shape function for the
Nonlocal equivalent plastic strain εpe,nl —
Automatic,
Linear,
Quadratic Lagrange, Quadratic serendipity,
Cubic Lagrange, Cubic serendipity,
Quartic Lagrange, Quartic serendipity, or
Quintic Lagrange. The available options depend on the order of the displacement field.
To display this section, click the Show More Options button (
) and select
Advanced Physics Options in the
Show More Options dialog box.
Select the Reduced integration check box to reduce the integration points for the weak contribution of the feature. Select a method for
Hourglass stabilization —
Automatic,
Manual, or
None to use in combination with the reduced integration scheme. The default
Automatic stabilization technique is based on the shape function and shape order of the displacement field.
Control the hourglass stabilization scheme by using the Manual option. Select
Shear stabilization (default) or
Volumetric stabilization.
When Shear stabilization is selected, enter a stabilization shear modulus,
Gstb. The value should be in the order of magnitude of the equivalent shear modulus.
When Volumetric stabilization is selected, enter a stabilization bulk modulus,
Kstb. The value should be in the order of magnitude of the equivalent bulk modulus.
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Maximum number of local iterations. To determine the maximum number of iteration in the Newton loop when solving the local plasticity equations. The default value is 25 iterations.
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Relative tolerance. To check the convergence of the local plasticity equations based on the step size in the Newton loop. The final tolerance is computed based on the current solution of the local variable and the entered value. The default value is 1e-6.
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To display this section, click the Show More Options button (
) and select
Advanced Physics Options in the
Show More Options dialog box.
Physics tab with Solid Mechanics selected: